Living Science Solutions for Class 8 Science Chapter 15 Chemical Effects Of Electric Current are provided here with simple step-by-step explanations. These solutions for Chemical Effects Of Electric Current are extremely popular among Class 8 students for Science Chemical Effects Of Electric Current Solutions come handy for quickly completing your homework and preparing for exams. All questions and answers from the Living Science Book of Class 8 Science Chapter 15 are provided here for you for free. You will also love the ad-free experience on Meritnation’s Living Science Solutions. All Living Science Solutions for class Class 8 Science are prepared by experts and are 100% accurate.

Page No 196:

Question 1:

Electric current is the flow of particles with
(a) a negative charge.
(b) a positive charge.
(c) both positive and negative charges flowing opposite to each other.
(d) either positive or negative charge depending on the material.

Answer:

d) either positive or negative charge depending on the material

In a solid conductor (copper wire, aluminium wire, etc.), current is the flow of negative charges (electrons). The direction of current is opposite to the direction of electrons. In a liquid conductor (a salt solution), current is the flow of positive ions (positive charges). Flow of current is the same as the direction of positive ions, but opposite to the direction of negative ions.

Page No 196:

Question 2:

Which of the following is not a conductor of electricity?
(a) tap water
(b) salt water
(c) pertol
(d) lime juice

Answer:

(c) petrol

Petrol is a hydrocarbon; therefore, it does not have free electrons or ions to conduct electricity.

Page No 196:

Question 3:

An electrolyte is a
(a) solid that conducts electricity.
(b) liquid that conducts electricity and breaks up chemically in the process.
(c) liquid that does not conduct electricity.
(d) solid that does not conduct electricity.

Answer:

(b) liquid that conducts electricity and breaks up chemically in the process

A substance that conducts electricity in its liquid state or when dissolved in water, and breaks up chemically during the process is called an electrolyte.

Page No 196:

Question 4:

On passing electricity through copper sulphate solution.
(a) copper is formed at anode.
(b) copper is formed at cathode.
(c) oxygen is formed at anode.
(d) hydrogen is formed at cathode.

Answer:

(b) copper is formed at cathode.

On passing electricity through copper sulphate solution, the salt ionizes to its constituent ions in the solution. These ions travel towards the oppositely charged cathode, i.e. copper, while the sulphate ions travel towards the anode thereby conducting electricity.

Page No 196:

Question 5:

In which of these is current not conducted by electrons?
(a) copper
(b) aluminium
(c) tap water
(d) mercury

Answer:

(c) tap water

In tap water, the current is not conducted by ions.

Page No 196:

Question 6:

Which of these metals will you electroplate on iron to protect it from rusting and to make it shine?
(a) copper
(b) gold
(c) zinc
(d) chromium

Answer:

(c) zinc

Iron is coated with zinc to protect it from corrosion and formation of rust. The zinc coating will also give it a shiny appearance.

Page No 196:

Question 1:

A positively-charged body has a __________ (deficit/excess) of electrons.

Answer:

A positively-charged body has a deficit of electrons.

Page No 196:

Question 2:

Electronic current flows from positive to negative. True or false?

Answer:

False.
Since electrons flow from a negatively charged body (excess of electrons) to a positively charged one (deficit of electrons), electronic current will also flow from the negative to the positive charge.

Page No 196:

Question 3:

A battery is used as a driving force in an electric circuit. True or false?

Answer:

True.

Electromotive force is the driving force in an electric circuit, which pushes the electrons carrying the charge around the circuit. This force is created by an electric cell or a battery.

Page No 196:

Question 4:

which of these particles are responsible for the flow of electric current−electrons, protons or neutrons?

Answer:

Electrons are responsible for the flow of electric current. They flow from a negatively charge body (with excess of electrons) to a positively charged one (with deficit of electrons).

Page No 196:

Question 5:

Metals are conductors of electricity. True or false?

Answer:

True.

Metals are conductors of electricity, as they allow electric current to flow through them.

Page No 196:

Question 6:

Which of these is better for use in a tester for testing conductivity of liquids−electric bulb or LED light?

Answer:

LED light is better for use in a tester for testing conductivity of liquids because it lights up even with a small amount of current.

Page No 196:

Question 7:

Most liquids that conduct electricity are solutions of __________, __________ or __________

Answer:

Most liquids that conduct electricity are solutions of acids, bases or salts.

Page No 196:

Question 8:

When electricity is passed through tap water, the gases __________ and __________ are evolved.

Answer:

When electricity is passed through tap water, the gases hydrogen and oxygen are evolved.

Page No 196:

Question 9:

Ions may be positively charged or negatively charged. True or false?

Answer:

True.
Ions may be positively charged or negatively charged. Positively charged ions are called cations, while the negatively charged ions are called anions.

Page No 196:

Question 10:

An electric current brings about chemical changes in most conducting __________ (solids/liquids).

Answer:

An electric current brings about chemical changes in most conducting liquids.



Page No 197:

Question 1:

How will you show experimentally that an electric current can bring about a chemical change? What is this phenomenon called?

Answer:

When copper sulphate is dissolved in water, it breaks into positively charged ions (cations) and negatively charged ions (anions).
Cations move towards the negatively charged electrode (cathode), and anions move towards the positively charged electrode (anode), thereby depositing copper at the cathode. This experiment shows that an electric current can bring about a chemical change and the phenomenon is called electrolysis.

Page No 197:

Question 2:

What is electroplating? How will you carry out electroplating of copper in the laboratory?

Answer:

Electroplating is the process of coating a thin layer of a metal such as gold, silver, chromium, etc., over another metal.
This is done to protect the metal or to lend it an attractive look.
For electroplating copper in the laboratory, the following steps are to be taken:

  • Fill three-forth of a beaker with copper sulphate solution.
  • Hammer a copper wire to flatten it; then connect it to the positive terminal of a battery.
  • Connect a spoon to the negative terminal of the battery.
  • Dip the copper wire as well as the spoon in the copper sulphate solution, and let the current pass.
At the end of this experiment, you will observe a layer of copper formed over the spoon.

Page No 197:

Question 3:

List four uses of electroplating, giving the reason for electroplating in each case.

Answer:

Four uses of electroplating are:

  1. Iron used to make bridges and automobiles is electroplated with zinc in order to prevent rusting.
  2. Gold or silver is electroplated on jewellery made from a cheaper metal in order to make the jewellery look attractive.
  3. Iron used to make food-storage utensils is electroplated with tin to prevent the food from getting spoiled by reacting with iron.
  4. Chromium is a shiny metal that never corrodes and also resists scratches. It is electroplated on a cheaper metal like iron to make it corrosion and scratch-resistant. Chromium-plated iron is used for manufacturing car parts, wheel rims, taps, etc.

Page No 197:

Question 11:

During electroplating, copper is deposited at the __________ (anode/cathode).

Answer:

During electroplating, copper is deposited at the cathode.

Page No 197:

Question 12:

Expensive metals are protected by electroplating. True or false?

Answer:

False.
Objects made from less expensive metals are electroplated with expensive metals, so that they look more attractive and beautiful.

Page No 197:

Question 1:

Which of these uses less electrical energy − electric bulb or LED light?

Answer:

An LED light consumes less electrical energy than an electric bulb.

Page No 197:

Question 2:

Mercury is a liquid and conducts electricity. Do you think it is an electrolyte?
(HINT: Mercury is a metal that is a liquid at room temperature.)

Answer:

No.
Neither mercury produce ions in a solution nor in its liquid state; therefore, it cannot be used as an electrolyte. However, it has free electrons that can well-conduct electricity.

Page No 197:

Question 3:

Solid copper sulphate does not conduct electricity, but when it is dissolved in water, it does conduct electricity. Why?

Answer:

One of the essential requirements for conducting electricity is the presence of free electrons or ions. In its solid state, the ions of copper sulphate (ionic compound) are immobile; therefore, it cannot conduct electricity. But when it is dissolved in water, it dissociates into copper ions and sulphate ions. These dissociated ions of copper sulphate conduct electricity.

Page No 197:

Question 4:

Copper conducts electricity through electrons, whereas salt solution conducts electricity through ions. Do you agree?

Answer:

Yes, we agree that copper conducts electricity through electrons, while a salt solution conducts electricity through ions.
Copper is a metal and has free electrons to conduct electricity, whereas a salt solution is an electrolytic solution. The salt ionizes into its constituent ions in the solution. These ions travel towards the oppositely charged electrodes and conduct electricity.

Page No 197:

Question 5:

Why should you not touch electrical appliances with wet hands?

Answer:

Water is a good conductor of electricity. So, if a person touches an electrical appliance with wet hands, he/she may get electrocuted.

Page No 197:

Question 6:

After doing Activity 5 (electroplating a spoon with copper), a student interchanged the connections of the copper plate and the spoon.  What do you think will happen now?

Answer:

If a student interchanges between the copper wire and the spoon during electroplating, the copper ions deposited on the spoon will move back to their place of origin.

Page No 197:

Question 7:

We should not try to put out a fire in an electrical appliance by pouring water on it. Why?

Answer:

Water is a good conductor of electricity. Therefore, if we pour water in order to put out a fire in an electric appliance, we may get electrocuted. So, we should not use water to put out a fire in an electric appliance.

Page No 197:

Question 8:

Instead of taking the trouble of electroplating metals with chromium for making car parts, taps, cycle parts, etc. why are these objects not made of chromium itself?

Answer:

Different metals have different properties and on the basis of these properties they are used. Chromium is only used for electroplating metals in order to increase their life span. Besides this, chromium is expensive. So, instead of making the whole item with chromium, a layer of chromium is only added to lend a lustrous look to the item.

Page No 197:

Question 1:

What is electric current?

Answer:

A continuous and directed flow of negative charges (i.e. electrons) through a wire is called electric current.

Page No 197:

Question 2:

How is electronic current different from conventional current?

Answer:

Conventional current flows from a positively charged body to a negatively charged one, while the electronic current flows from a negatively charged body to a positively charged one. This is the difference between electronic current and conventional current. 

Page No 197:

Question 3:

Differentiate between conductors and insulators.

Answer:

 

Conductors Insulators
A conductor allows the electric current to flow through it when a potential difference is applied across its ends. An insulator does not conduct electricity unless extremely high potential difference is applied across its ends.
A good conductor of electricity is generally a good conductor of heat. Insulators do not conduct heat.
Conductors have free electrons on its surface. Insulators have bonded electrons on its surface.

Page No 197:

Question 4:

What is an electrolyte?

Answer:

A substance which conducts electricity in its liquid state or when it is dissolved in water to break-up chemically is called an electrolyte. Most soluble salts, acids and bases are electrolytes. Some examples are NaCl, KCl, NaOH, etc.
 

 

Page No 197:

Question 5:

Why is zinc electroplated on iron?

Answer:

Electroplating means coating a thin layer of a metal over another metal.
Zinc is electroplated on iron to prevent the latter from rusting. Hence, iron electroplated with zinc has various applications in the construction and automobile industries.

Page No 197:

Question 1:

Draw a circuit diagram showing a dry cell connected to a bulb through a switch. Mark the positive and negative terminals of the cell and the direction of flow of
(a) electrons
(b) conventional current

Answer:



(a) The electrons will flow from the negative to the positive terminal.
(b) Conventional current will from from the positive to the negative terminal.

Page No 197:

Question 2:

What are the advantages of electroplating iron with chromium?

Answer:

Chromium is a shiny metal that never corrodes and also resists scratches. Therefore, it is electroplated on iron to make it scratch-resistant and free from corrosion.

Page No 197:

Question 3:

Discuss what happens when an electrolyte is dissolved in water, and then an electric current is passed through it.

Answer:

When an electrolyte is dissolved in water, it breaks into cations (positively charged ions) and anions (negatively charged ions).
These ions then move freely in the aqueous solution. When an electric current is passed through this solution, the cations move towards the negatively charged electrode, i.e. the cathode, and the anions move towards the positively charged electrode, i.e. the anode.

Page No 197:

Question 4:

What happens when electricity is passed through tap water?

Answer:

Tap water is impure and contains salts of metals dissolved in it. Therefore, when electricity is passed through tap water, it will start conducting the electricity.



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